The broad, long-term objective of this proposal is to understand neuronal mechanisms by which animals process sensory information and accordingly generate adaptive behavior. Of particular interest is how animals generate diverse behaviors using limited sets of motor circuits. The proposed study is designed to elucidate the neuronal mechanisms underlying a variety of electrical behaviors performed by an electric fish, Hypopomus, during courtship and aggression. It was recently discovered that a variety of behaviors can be induced in a curarized preparation of this electric fish by microiontophoresis of L-glutamate into a small region in the diencephalon, the prepacemaker nucleus. The first two specific aims are to understand how different behaviors are organized in this small brain structure. Physiological recordings and anatomical labeling will be performed in in vivo preparations. The prepacemaker nucleus projects to the final motor nucleus, the pacemaker nucleus, and modulates its regular oscillation to generate electrical behaviors. The following two specific aims are to understand how the pacemaker nucleus generates complex motor outputs. Despite its very simple organization and the rigid electrical coupling between constituent neurons, the pacemaker nucleus is capable of generating a variety of outputs under the modulatory inputs from the prepacemaker nucleus. In vivo preparations will also be used for intracellular penetration of pacemaker neurons while behaviors are induced by stimulation of the prepacemaker nucleus. The results of these experiments will contribute to the understanding of how the central nervous system regulates different types of behavior at the single-neuron level and how seemingly rigid networks can be modulated to generate different patterns of vertebrate behavior.